I agree mostly with longrifle1000! It looks to me as if the buck tripped while comming down the hill these pictures took place on, his left antler
caught the smaller tree spinning him around and possibly breaking his neck! If he was running from something the force would more than likely broken his neck. I believe this because if you look at the topography of the surrounding area a buck would not be tall enough to rub that tree from the downhillside and rubbing from the uphill side seems unethical. besides there is little evidence on the smaller tree to justify that rubbing had taken place. simply catching an antler in the tree while passing by seems shotty to me also because deer have an uncanny sense of their surroundings ( for instance deer bolting away in the dark and never touching a thing) second I find it unbelievable that a buck such as this one would not have finangled his way out if he had the power to do so! That is just my two cents however